Many types of communications can be performed over data networks (wireless and/or wireline networks), including electronic mail, web browsing, file downloads, electronic commerce transactions, voice or other forms of real-time, interactive communications, and others. To enable the establishment of communications sessions in a network, various control functions are deployed in the network. Some standards bodies have defined subsystems within communications networks that include such control functions. One such standards body is the Third Generation Partnership Project (3GPP), which has defined an Internet protocol (IP) multimedia subsystem (IMS) that includes various control functions for provision of IP multimedia services, including audio, video, text, chat, or any combination of the foregoing.
An IP multimedia subsystem can be used in conjunction with a wireless network, such as a wireless network according to the GSM (Global System for Mobile) or UMTS (Universal Mobile Telecommunications System) standard, as defined by 3GPP, or a wireless network according to CDMA 2000 (Code Division Multiple Access 2000), as defined by 3GPP2. An IP multimedia subsystem can also be used with wireline networks. In the 3GPP2 context, the equivalent of the IP multimedia subsystem is sometimes referred to as a multimedia domain (MMD) network. In the wireline context, the equivalent of an IP multimedia subsystem is sometimes referred to as a Next Generation Networks (NGN).
When a mobile station roams to a visited network, signaling messages exchanged with the roaming mobile station can be communicated between the visited network and a home network of the mobile station. The visited network and home network are usually provided by different service providers. Therefore, security is a concern between the visited network and the home network, since it would be undesirable for the home network to be able to learn network topology information associated with the visited network based on the exchanged signaling messages of the mobile station. To address this, topology hiding is typically performed, such as by providing an IMS application level gateway (ALG), sometimes referred to as a topology hiding internetwork gateway (THIG), in a proxy call session control function (P-CSCF) or interconnect border control function (IBCF) of the IMS network. The P-CSCF and IBCF are part of the call signaling interface between the visited network and the home network. The IMS ALG implemented in the P-CSCF or IBCF is used to obscure network topology information of the visited network for the call signaling interface.
However, an issue that has arisen is that the topology hiding provided by the IMS ALG is often insufficient to protect network topology information.